1. Field of the Invention
The present invention relates to a shutter for use in a camera.
2. Description of the Related Art
FIG. 7 shows, in exploded form, a conventional type of focal plane shutter for use in a camera.
Referring to FIG. 7, a shutter base plate is represented by numeral 1, and blade driving lever shafts 2 and 2' have main arm bearing shafts 2a and 2a', respectively, each of which is formed at one end of each of the blade driving lever shafts 2 and 2'. A charge lever shaft 3 serves as a pivot axis for rotatably supporting a charge lever (not shown) which causes the blade driving lever shafts 2 and 2' to rotate in the shutter charging direction. Auxiliary arm bearing shafts 4 and 4' are disposed for pivotally supporting corresponding auxiliary arms which will be described later. A cover plate 13 is mounted on the shutter base plate 1 by means of shafts 5, 6a, 6b and 6c. The shutter base plate 1 has an aperture 7, holes 8a to 8i and arcuate slots 9 and 9'. The above-noted shafts 2, 2', 3, 4, 4', 5, 6a, 6b and 6c are respectively fitted into the holes 8a to 8i and fixed to the shutter base plate 1 by caulking. The arcuate slots 9 and 9' are formed so as to correspond to the range of swinging motion of the charge lever (not shown). A leading blade group 10 includes a slit forming blade 10c and separate blades 10d. These blades 10c and 10d are linked by a main arm 10a and an auxiliary arm 10b at caulked portions 10e and 10e', respectively. The main arm 10a is supported for pivotal movement about the main arm bearing shaft 2a of the blade driving lever shaft 2, while the auxiliary arm 10b is supported for pivotal movement about the auxiliary arm bearing shaft 4. A trailing blade group 11 includes a slit forming blade 11c and separate blades 11d. These blades 11c and 11d are linked by a main arm 11a and an auxiliary arm 11b at caulked portions 11e and 11e', respectively. The main arm 11a is supported for pivotal movement about the main arm bearing shaft 2a'of the blade driving lever shaft 2', while the auxiliary arm 11b is supported for pivotal movement about the auxiliary arm bearing shaft 4'. A partition plate 12 is sandwiched between the leading blade group 10 and the trailing blade group 11 so as to prevent the two groups from interfering with each other. The partition plate 12 also has an aperture 12a which corresponds to the aperture 7. The cover plate 13 is formed from a thin metal sheet similarly to the shutter base plate 1 and has an aperture 13a which corresponds to the aperture 7. Spacers 14 and 15 for assuring smooth running of the leading and trailing blade groups 10 and 11 respectively are disposed on the opposite sides of the partition plate 12 and at locations over which the free end portions of the blades 10c, 10d and 11c, 11d slide.
However, such a conventional shutter structure presents the following problem. As described previously, the blade driving lever shafts 2 and 2', the charge lever shaft 3, the auxiliary arm bearing shafts 4 and 4' and the shafts 5, 6a, 6b and 6c are respectively fitted into the hole 8a to 8i in the shutter base plate 1 and fixed thereto by caulking. Therefore, production of such a shutter base plate unit requires a time-consuming and costly working process.
In order to reduce the cost and simplify the production process, such a shutter base plate may be formed of a synthetic resin and, at the same time, the above-described individual shafts may be integrally formed. However, this method involves the following disadvantages. If a large force is applied to such a synthetic resin-molded portion through the blade driving levers, the charge lever or other parts, deformation may occur in the molded portion owing to the force and more or less affect the running of each blade group. It would follow that the accuracy of exposure based on a shutter opening and closing operation (shutter speed) could not be assured. At worst, the shutter base plate might be broken due to lack of physical strength.
The present applicant previously proposed a synthetic resin-molded shutter base plate integral with individual shafts in Japanese Laid-Open Utility Model Application No. Sho 58-16625 (U.S. Patent not applied for). This proposal discloses one embodiment which includes a structure constituted by a combination of a resin molding and intimately superimposed press-cut metal sheets and another embodiment which includes a structure constituted by a combination of a resin molding and an insert-molded metal sheet, both embodiments increasing the physical strength of the shutter base plate. However, this proposal does not disclose any method of solving the previously-described problems with the shutter base plate formed of a synthetic resin alone.
The conventional shutter structure shown in FIG. 7 further involves the following problem. As shown in FIG. 8 which is a schematic sectional view of a portion including the apertures, gaps may be formed between adjacent blades 11c and 11d when the trailing blade group 11 is in an unfolded state. This could result in a problem such as the deterioration of the light shielding performance of the shutter. To cope with this problem, it has been necessary to adopt a special arrangement which requires a time-consuming production process.
In addition, the shutter base plate 1 shown in FIG. 7 involves the following disadvantages. In order to assure smooth running of the blades, the shutter base plate 1 must be subjected to secondary working such as formation of a chamfer 7a (such as that shown in FIG. 9) on an edge portion which faces the aperture 7. Furthermore, since the shutter base plate 1 is made of a metal material and has the aperture 7 defined by flat end surfaces, harmful light of significant intensity may be reflected by the flat end surfaces. As a result, there is a risk that the film accommodated in the camera may be adversely influenced.
Such an adverse influence will be described in detail below with reference to FIG. 9. The camera shutter shown in FIG. 7 is arranged so that the shutter base plate 1 may be mounted on the front plate unit of a camera body (not shown). Therefore, harmful light 71 passing through a photographing lens falls on the shutter base plate 1 and, in turn, is reflected from a flat end surface 7b facing the aperture 7 in the shutter base plate 1 to become reflected light 72 which reaches a film 50 located behind the cover plate 13.
For this reason, the conventional type of shutter structure requires a heavy anti-reflection coating which, even when applied, has been found incapable of completely eliminating the harmful reflected light.